1. Field of the Invention
The present invention relates to a voice coil module (VCM), and more particularly, to a VCM used for lens fixation and displacement measurement in order to prevent and control power consumption.
2. Description of the Related Art
A voice coil module (VCM) generally includes a permanent magnet and a coil. An attractive force or a repulsive force is produced between an induced magnetic field generated by a current flowing through the coil and a magnetic filed generated by the permanent magnet. Displacement of a lens occurs due to a spring force as well as the attractive force or the repulsive force.
The VCM advantageously has a simple structure and a low manufacturing cost. Therefore, the VCM is widely used in a driving unit of an automatic focusing device provided to a small image sensor. The driving unit of the automatic focusing device may be implemented with a stepping motor or an ultrasonic motor.
Manufacturing of a small stepping motor requires a high cost and a difficult technique. Therefore, a small automatic focusing device is generally driven by using the ultrasonic motor or the VCM.
FIG. 1 illustrates a structure of a conventional VCM.
A lens 110 is fixed to a vertically movable lens barrel 120. A coil 140 that generates a magnetic field in response to an input current is disposed to the lens barrel 120. The lens barrel 120 is connected with a casing 130 and a spring 150. A permanent magnet 160 is fixed to the casing 130. A current 180 is supplied to the coil 140 through an input terminal 170 while changing its direction and magnitude. In this case, the lens barrel 120 moves to an equilibrium point between a spring force and a magnetic force exerted between the permanent magnet 160 and the coil 140.
According to the magnitude and direction of the input current, a displacement 190 of the lens barrel 120 is regulated. In the VCM having this structure, a current having a constant magnitude and direction has to be continuously provided so that the lens 110 can maintain a constant position, resulting in a significant amount of power loss.
That is, although the VCM can be manufactured in a small size due to its cost competitiveness, simply operation, and simple structure, the conventional VCM has a demerit in that power loss is more significant than the ultrasonic motor since, in order to fix the lens 110 to a specific position, a constant current has to be continuously supplied to a driving coil. Such power loss is a major stumbling block when it comes to put the VCM to the market for a small-sized product using a battery.
Furthermore, the conventional VCM is not provided with a method for determining whether the VCM is correctly controlled and for measuring a present position of the VCM. Therefore, a problem lies in that it is difficult to accurately control the VCM, and an erroneous operation cannot be prevented.